Image recording medium and process

ABSTRACT

An electron and/or photon sensitive soluble copper salt in solution is coated upon a substrate, with subsequent evaporation of its solvent. For substrates which resist wetting by the copper salt solution, a wetting agent or film former is employed to obtain an even copper salt coating. For cases where the medium is to be electron exposed, resistivity of the medium is maintained at a sufficiently low level by an additional coating of adequately low resistivity applied beneath the cooper salt layer. After electron or photon exposure, the latent image is developed by exposing the latent image to metal vapor. Thereupon a stable and visible image is formed. The optical density of the image is proportional to the exposure. When the substrate is transparent, this image can be employed in projection.

United States Patent [1 1 McKee et al.

[ 1 IMAGE RECORDING MEDIUM-AND PROCESS [75] Inventors: William E. McKee,Woodland Hills;

Erika E. Kaspaul, Malibu, both of Calif.

[73] Assignees Hughes Aircraft Company, Culver City, Calif.

22 Filed: May 28,1969

21 Appl. No.: 828,572

OTHER PUBLICATIONS Light-Sensitive Systems, Jaromir Kosar, pp. l4, 15,

[451 Feb. 5, 1974 Allen A Dicke, Jr.

57 ABSTRACT An electron and/or photon sensitive soluble copper salt insolution is coated upon a substrate, with subsequent evaporation of itssolvent. For substrates which resist wetting by the copper saltsolution, a wetting agent or film former is employed to obtain an evencopper salt coating. For cases where the medium is to be electronexposed, resistivity of the medium is maintained at a sufficiently lowlevel by an additional coating of adequately low resistivity appliedbeneath the cooper salt layer. After electron or photon exposure, thelatent image is developed by exposing the latent image to metal vapor.Thereupon a stable and visible image is formed. The optical density ofthe image is proportional to the exposure. When the substrate istransparent, this image can be employed in projection.

6 Claims, 2 Drawing Figures IMAGE RECORDING MEDIUM AND PROCESSBACKGROUND This invention is directed to image recording, andparticularly to the recording and near real time projection of images ontransparent substrates.

In image recording, silver halide recording is wellknown. Silver halideemulsions can be formulated to be particularly sensitive to electronbeam recording,'and thus such emulsions are useful to perform recordingand projection steps. However, silver halide emulsions require wetdevelopment which prevent them from being satisfactory for situations inwhich projection is required in near real time.

A medium which is capable of near real time projection is that in whicha film is employed, the surface of which is heat deformable in acontrolled manner by the electric charge deposited on the film by anelectron beam. These are often called thermoplastic films. However, suchfilms require schlieren optics, which consume at least 50 percent of theprojector output. This inefficiency leads to careful design to preventfilm overheating, and leads to lesser screen illumination.

SUMMARY In order to aid in the understanding of this invention, it canbe stated in essentially summary'form that it is directed to an imagerecording medium and process. The medium employs a soluble sensitivecopper salt deposited on a substrate from solution, which deposit layeris sensitive to photon and/or electron exposure. After exposure, thelatent image created by the exposure is developed by the imagewisedeposition of metal from vapor. The imagewise deposition of metalproduces a visible image. When the substrate is transparent, the imagecan be used for projection. The optical density of the image intransmission is substantially proportional to the exposure so thatcontinuous tone images are possible.

Accordingly, it is an object of this invention to provide an imagerecording medium and process wherein an image can be produced'byirradiating a deposited soluble sensitiveflcopper salt layer, followedby metal vapor development. It is another object to provide an imagerecording medium which has a substantially transparent substrate and hasan image recording copper salt layer deposited thereon, which layer issubstantially transparent until a visible image is developed thereon, sothat the medium can be employed in projection. It is a further object toprovide an image recording medium which is stable and has a long life inordinary atmospheres so long as the light level is minimized, until itis exposed and developed, and thereafter has a long life in an openatmosphere. It is a further object to provide an image recording mediumwhich comprises the deposition of the copper salt from a copper saltsolution on a substrate, and where the substrate is hydrophobic,includes the employment of a wetting agent or a film former. It is stillanother object to provide an image recording medium on a conductivecoating where the image recording medium is to be employed in electronbeam recording so that the electron beam charge can be dissipated, andwherein the confduc'tive layer is substantially transparent so as not tohinder the projectability of the developed image. It is still anotherobject to employ copper compounds which are stable in an atmosphericenvironment, and

which are soluble so that they can be deposited upon a substrate fromsolution. It is another object to select a copper salt from those whichare soluble in water and those which are soluble in organic solvents,and to select copper salts which are stable in atmospheric environments.It is still another object to employ a copper salt witha film formerwherein the copper complexes directly with the film-forming polymer.

Other objects and advantages of this invention will become apparent fromthe study of the following portion of the specification, the claims andthe attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic perspective viewof the image recording medium of this invention.

FIG. 2 is a schematic sectional view illustrating the employment of themedium, and the process of this invention.

DESCRIPTION Referring to FIG. 2, shown therein is a schematic ofrecording and projection device 10 which employs the medium and processof this invention. Light-tight chamber 12 contains a roll 14 ofsubstrate 16 which is to be coated at coater 18.

The preferred use of the image recording medium is for projection, andthus the substrate 16 is substantially transparent. For convenience inhandling, it is preferable that the. substrate be flexible so that itcan be rolled. However, if flexibility is not required, glass is asatisfactory substrate. In the preferred embodiment of a flexiblesubstrate, any of the conventional types of transparent films aresatisfactory. Clear Cronar film, a polyester synthetic compositionmaterial, made by El. DuPont de Nemours, of Wilmington, Del., ispreferred, because it is conveniently available and is vacuum stable. Insome cases, as will become clearhereinafter, a substrate which ishydrophyllic, such as a polyester film with a gelatin-modified surface,known to the trade as subbed, is desirable. Other substrate, such ascellulose acetate and Nesa coated glass, are also useful in particularcircumstances, as is hereinafter described.

The sensitive layer is sensitive to both ultraviolet photons and toelectrons. When the medium is employed for photon exposure, there, is norequirement that electrons be conducted away. However, for electronexposure, the charge resulting from the electron beam must be conductedaway. This can be accomplished either by a suitable substrate or asuitable sensitive coating, or can be accomplished by the application ofa substantially transparent conductive coating 20. The electricalresistivity of the finished medium should be less than 1 megohm persquare, so that the character of the substrate 16 and the sensitivecoating determine the amount of conductive coating 20 required forelectron beam exposure applications. Examples of conductive coatings 20which have the highest light transmission are vacuum-deposited copperiodide, bismuthoxide-gold and, to a lesser extent, vacuum-depositedaluminum and chromium. In order to decrease the amount of conductivecoating 20 required, the conductivity of the sensitive coating mayitself be increased by the addition of antistatic compounds, such asStearamidopro-- Substrate 16, with or without conductive coating 20, asrequired, is supplied to coater l8. Coater 18 applies the sensitivecoating layer 22. The sensitive layer is a soluble copper salt. Thecopper salt has the requirement that it be soluble either in water or inorganic solvent; that it be stable in atmospheric oxygen and moisture;and that it be photon and/or electron sensitive. Organic solventsinclude acetone, toluene and alcohol. Water soluble copper salts includecopper bromide, copper chloride, copper sulfate, copper formate, copperacetate, copper proprionate, copper lactate and copper salts of2-hydroxyisobutyric acid, glycolic acid, 2-hydroxylauric acid andglyceric acid. Included in the class of organic solvent soluble coppersalts are copper salts of long-chain, fatty acids and complex organicacids consisting of oleic, linoleic, napthenic, stearic, undecylenic andbehenic acids; and coordination compounds consisting of copperacetylacetonate, Bis (ethyl acetoacetato) copper, Bis (l phenyl 1,3-butanediono),

and copper dimethyldithiocarbamate.

Whether or not a wetting agent or a polymeric filmforming material isemployed in the coater 18 for coating on the substrate 16 depends onwhether or not the copper solution wets the substrate, includingconductive coating 20, if there is one. In other words, if the coatingsolution does not smoothly coat the substrate, a film-forming materialor wetting agent must be added. When the substrate is hydrophyllic, suchas a gelatin modified polyester film, either water or organic solventdissolved copper salts will smoothly deposit. However, hydrophobicsubstrates, such as non gelatine modified polyester or glass, requirethe addition of a film former or a wetting agent. Water solublepolymeric film-forming materials, such as polyvinyl alcohol, hydroxypropylmethyl cellulose, carboxymethyl cellulose, polyethyleneimine, andorganic solvent solubles, such as the styrene-butadiene copolymers andacrylic type polymers are suitable. Such film-forming polymers improvethe spreading and coating of copper salt in solution on the substrateand serve to protect the deposited copper salt from abrasion.

After coating, the coated substrate goes to drying chamber 24 whereinthe solvent is removed from the coated layer. Drying can be accomplishedeither by forced hot air, or by evacuation, as illustrated in FIG. 2.After drying, the recording medium is complete and it can be stored,provided it is maintained at a low light level. Shelf life of the mediumis at least in the order of months. On the other hand, if desired, themedium may be immediately used.

The medium is illustrated as passing directly into exposure chamber 26.The copper salts listed are sensitive to photon exposure at about 3,000A. or less Angstroms wavelength, in the ultraviolet portion of thespectrum. Here it may be either exposed to photons or electrons. In thedrawing, scanning electron gun 28, which receives its signals fromsignal source 30, which provides signals in accordance with the desiredimage, directs a modulated electron beam 32 onto the sensi tive materialso that the image recording medium 34 is exposed. When only horizontaldeflection is provided to the electron beam, the image recording mediumcan be advanced at a constant rate to record such information as thatnormally contained in video signals. On the other hand, when bothvertical and horizontal deflection are provided, the image recordingmedium 34 can be advanced in stepwise fashion to expose one frame at atime. The earlier method is preferred, and suitable conventional meansfor proper rate of advance of the medium can be provided. Of course,scan speed and frame rates must be consistent with sensitivity of themedium so that adequate exposure occurs.

Exposure causes a latent image to be formed upon the sensitive materialof the image recording medium 34. After exposure, the image recordingmedium 34 is moved to development chamber 36 for development of thelatent image. Development is accomplished by exposing the latent imageto a source 38 of metal vapor. A suitable metal for development of thelatent image into a visible image having lesser transparency than theunexposed parts is zinc, which is preferred. However, mercury andcadmium are also believed suitable development metals. Development iscaused by suitable vaporization of the metal, as in a boat, to produce alow pressure of metal vapor, which then deposits metal selectively in animagewise fashion in thicknesses proportioned to the amount of exposure.Such an image is indicated at 39 in FIG. 1. For development of a fullyexposed image, and using zinc as the development metal, a zinc flux isdesired to produce a zinc layer having an optical density of about one,corresponding to a thickness of about 300-500 A. in the fully developeddensest areas. Such development produces a permanent image so thatexposure to light is not deleterious.

The copper compounds used in this invention must have certaincharacteristics and properties to produce the image formation process.The principal function is to provide 'a source of copper ions which canbe reduced by ultraviolet light or electrons to form metallic atomswhich further combine to form the stable nuclei which comprise thelatent image. These nuclei act as sites for further condensation ofmetal atoms from the metal vapor of the metal used as the imagedeveloper; for example, zinc. Each electron striking the sensitivesurface will produce a nucleation site upon which will condense, as anaverage, 10 to 10 metal atoms. In order to produce images capable ofprojection, the compound should be soluble in its carrier solution andbinder, so that it can be deposited in either a film of such minutethickness that it is transparent or as crystals of such small size thatthey are transparent. The carrier solution may be water, for watersoluble copper compounds, or an organic solvent appropriate to thesolubility of the compound.

After development, the developed image-recording medium can be storedfor later examination, or can be immediately passed to a suitablereading device. FIG. 2 illustrates the film going directly to projector40. Projector 40 includes light source 42, which includes propercondensing optics, projector housing 44 which includes properimage-recording medium, incremental advance and shutter mechanism, aswell as projection lens 46. In addition, screen 48 is provided forviewing. The projector 40 is a conventional transparency projector.

After projection, the image-recording medium can be rolled up ontostorage roll 50, or may be otherwise kept for later inspection orotherwise disposed of.

In view of the fact that the development metals usually deposit upon theexposed areas, a negative picture would conventionally result. Thus,signal source 30 is preferably arranged so that electron beam 32 causesmaximum exposure in the areas where it is desired that the finalprojected image be dark. This can be conventionally electronicallyaccomplished.

Examples of specific image recording media, and the I manner in whichthey were created, exposed, developed and its resultant opticalproperties are as follows:

EXAMPLE I surface was of the order of a megohm per square, but

was adequate to permit a surface conduction of the applied electrons. Ina vacuum chamber maintained at to 10 torr, latent images were producedin the layer of copper compound by exposure to an intensely modulatedelectron beam with a current of approximately 4 X 10" amps at lOkV. Theelectrons were deposited in a checkerboard pattern with alternating A;inch squares of exposed and unexposed surface. Varying the duration ofthe exposure time produced different electron dosages for each sample.For development of a visible image from the latent image, the sampleswere placed in another vacuum chamber which was then evacuated to 50 100torr. The temperature of an electrically heated zinc evaporation boatwas raised to 450 500C in 5 10 seconds and quickly cooled. The smallamount of zinc vapor produced during this time was absorbed selectivelyby the electron exposed areas while the unexposed areas remaineduncoated and transparent. A visible checkerboard image was obtained.Difference in the optical densities of the exposed and unexposed areaswas readily apparent, making optical projection possible. Transmissionoptical densities were measured on one sample which had received anelectron dosage of 6.1 X 10 coulombs/cm. The density difference betweenthe exposed and unexposed areas ranged from 1.3 to 1.4.

EXAMPLE II 1.25 gms of polyvinyl alcohol type 5l-05-DuPont weredissolved in 100 ml boiling water. To the cooled solution was added 0.25gms of cupric formate. Samples of 35 mm Cronar film leader were cut toapproximately 1% inch X 1% inch, dipped into this solution and allowedto dry overnight. The resistance was high, but surface conductivity wasenough to allow the charge to bleed off. A checkerboard test pattern wasapplied, as in Example I, and similarly zinc developed. The checkerboardimage developed showed a low background and a differential densitybetween background and image of 1.3 to 1.7 with an electron exposure ofapproximately 2.4 X 10 coulombs/cm? EXAMPLE III The same solution as inExample II was dipcoated .onto electrically conductive glass and driedovernight board pattern, as in Example I, with 3.2 X 10 coulombs atIOkV, and subsequently developed with zinc vapor, as in Example I,produced a measured differential optical density of 2.1 to 2.8. Exposureto 8.5 X 10 coulombs of electrons and zinc vapor development in asimilar manner produced differential densities of 1.9 to 2.2.

EXAMPLE IV The same solution as in Example II was applied to Cronar filmwhich had been coated with a transparent, conductive layer ofcodeposited gold-bismuth having a surface resistance of 15-10ohms/square. In this case, electron exposure and development, as inExample I, with 2.2 to 10 coulombs/cm gave a differential density of2.7. Exposure to l X 10 coulombs/cm gave a differential density of 2.0.Exposure to 0.7 X 10 coulombs/cm gave a differential density of 1.1.Exposure to 0.3 X 10 coulombs/cm gave 0.7 density.

EXAMPLE V The same solution as in Example II was applied to a Cronarfilm, which had been coated with a transparent, conductive cuprousiodide coating having a resistance of about 2,500 ohms/square. Electronexposure to 3.8 X 10 coulombs/cm and development, as in Example I,produced a differential density of 2.3.

EXAMPLE VI One gram of hydroxyl propyl methyl cellulose and 0.5 gram ofcupric formate were dissolved in ml H O. This solution was dipcoated onclear Cronar without application of conductive subcoating. Exposure to 5X 10 coulombs/cm at lOkV and development, as in Example I, produced amaximum density differential of 0.9. Surface resistance was very high,but sufficient to permit electrons to leak away from the exposed areasto ground.

EXAMPLE VII 0.119 gms of bis (ethyl) acetoacetato copper were dissolvedin 100 ml. of toluene containing 0.3 gms of 30 percent by weight ofGoodyear Tire and Rubber Co. Pliolite S-7 (a polystyrene budadienecopolymer). This solution was coated by immersion of 35 mm perforatedpolyster film with trade name Cronar. After evaporation of solvent,exposure of the film to light in total quantity of about 18 X 10 ergs/cmfrom a low pressure mercury arc (maximum output at 2,537A.) during aperiod of 3 minutes through a metal mask with imagewise openingsproduced a latent image which could be developed to a visible image byexposure to zinc vapor, as in Example 1. Maximum density differentialbetween exposed and unexposed areas was 1.0. The exposed areas wereclear while the unexposed areas became dark. This represents a positiveimage.

EXAMPLE VIII 0.049 gms of copper acetyl acetonate was dissolved in 100ml of toluene containing 0.3 gms of Rohm and Haas Acroyloid B-72solution (an acrylic type polymer). The solution was coated on film, asin Example VII, and similarly exposed and developed with zinc vapor, asin Example I. In this case, a negative image was produced. The exposedareas were dark and visible while the unexposed areas remained clear.The differential densities'were not measured.

This invention having been described in its preferred embodiment, it isclear that it is susceptible to numerous modifications and embodimentswithin the ability of those skilled in the art and without the exerciseof the inventive faculty. Accordingly, the scope of this invention isdefined by the scope of the following claims.

What is claimed is:

1. An image-recording medium, recording medium comprising:

a transparent substrate;

the active ingredient of said medium consisting essentially of aradiation sensitive, liquid-soluble, transparent precipitatedcrystalline copper salt on said substrate to form a transparentuncoated, reducing-agent-free, electron-sensitive layer on saidsubstrate, said copper salt being unchanged in transparency uponexposure and being reducible by electron impingement to produce copperatoms which combine to form stable nuclei which comprise a latent image,said substrate and said sensitive layer having a resistivity less than 1megohm per square.

2. The image-recording medium of claim 1 wherein said copper salt is awater-soluble salt of copper in the valence 2 state selected from thegroup consisting of cupric bromide, cupric chloride, cupric sulfate,cupric formate, cupric acetate, cupric proprionate, cupric lactate andcopper salts of 2-hydroxyisobutyric acid, glycolic acid, 2-hydroxylauricacid, and glyceric acid.

3. The image-recording medium of claim 1 wherein said copper salt is anorganic solvent soluble salt of copper in the valence 2 state selectedfrom the group consisting of copper salts of long-chain, fatty acids andcomplex organic acids consisting of oleic, linoleic, napthenic, stearic,undecylenic and behenic acids; and coordination compounds consisting ofcopper acetylacetonate, Bis (ethyl acetoacetato) copper, Bis (1 phenyll, 3-butanediono), and copper dimethyldi said imagethiocarbamate.

4. The image-recording medium of claim 3 wherein a conductive layer ispositioned between the substrate and the sensitive layer, saidconductive layer being substantially visually transparent and providingresistivity of said medium below about 1 megohm per square.

5. The process of recording an image, said process comprising the stepsof:

providing a transparent substrate; dissolving essentially only a solublecopper salt which is sensitive to electron and photon radiation exposurein a liquid solvent to form a liquid solution consisting essentially ofsolvent and copper salt;

coating the substrate with the liquid solution of radiation sensitivesoluble copper salt;

evaporating the solvent to provide a transparent deposited layer, theactive ingredient consisting essentially of radiation sensitive coppersalt on the substrate;

imagewise exposingby electron or photon impinge-.

ment the image-sensitive copper salt layer to provide a latent imageconfigured in accordance with the exposure;

developing the latent image by directing an elemental metal vapor fluxof a metal which is less noble than copper at the latent image-carryingcopper salt layer in subatmospheric pressure so that the elemental metaldeposits as a solid in accordance with the latent image on the sensitivecopper salt layer to produce a visible image.

.6. The process of claim 5 further including the succeeding step of:

projecting light onto the metal-developed, imagecarrying substrate sothat light passes through the substrate where no development metal hasbeen image-wise deposited to project an image configured in accordancewith the exposure step.

2. The image-recording medium of claim 1 wherein said copper salt is awater-soluble salt of copper in the valence 2 state selected from thegroup consisting of cupric bromide, cupric chloride, cupric sulfate,cupric formate, cupric acetate, cupric proprionate, cupric lactate andcopper salts of 2-hydroxyisobutyric acid, glycolic acid, 2-hydroxylauricacid, and glyceric acid.
 3. The image-recording medium of claim 1wherein said copper salt is an organic solvent soluble salt of copper inthe valence 2 state selected from the group consisting of copper saltsof long-chain, fatty acids and complex organic acids consisting ofoleic, linoleic, napthenic, stearic, undecylenic and behenic acids; andcoordination compounds consisting of copper acetylacetonate, Bis (ethylacetoacetAto) copper, Bis (1 phenyl 1, 3-butanediono), and copperdimethyldithiocarbamate.
 4. The image-recording medium of claim 3wherein a conductive layer is positioned between the substrate and thesensitive layer, said conductive layer being substantially visuallytransparent and providing resistivity of said medium below about 1megohm per square.
 5. The process of recording an image, said processcomprising the steps of: providing a transparent substrate; dissolvingessentially only a soluble copper salt which is sensitive to electronand photon radiation exposure in a liquid solvent to form a liquidsolution consisting essentially of solvent and copper salt; coating thesubstrate with the liquid solution of radiation sensitive soluble coppersalt; evaporating the solvent to provide a transparent deposited layer,the active ingredient consisting essentially of radiation sensitivecopper salt on the substrate; imagewise exposing by electron or photonimpingement the image-sensitive copper salt layer to provide a latentimage configured in accordance with the exposure; developing the latentimage by directing an elemental metal vapor flux of a metal which isless noble than copper at the latent image-carrying copper salt layer insubatmospheric pressure so that the elemental metal deposits as a solidin accordance with the latent image on the sensitive copper salt layerto produce a visible image.
 6. The process of claim 5 further includingthe succeeding step of: projecting light onto the metal-developed,image-carrying substrate so that light passes through the substratewhere no development metal has been image-wise deposited to project animage configured in accordance with the exposure step.